The lysozyme from bacteriophage T4 will be used as a model system to understand the factors that determine the folding, stability, activity and three-dimensional structures of proteins. The specific research to be accomplished is as follows: 1. Mutant lysozymes with altered stability (and/or catalytic activity) will be selected and studied in detail. These mutant lysozymes will include not only temperature-sensitive lysozymes but also lysozymes that are more thermally stable than the wild-type enzyme. The three-dimensional structures of these mutant lysozymes will be determined and compared with the wild-type lysozyme structure. Changes in structure will be correlated with changes in stability and activity. 2. Oligonucleotide-directed mutagenesis will be used to introduce designed alterations in the lysozyme structure. By making a series of selected amino acid replacements at one site we will discriminate between the contributions of different interactions at that site. Site-directed mutagenesis will also be used to test the importance of factors such as hydrogen bonding, secondary structure stabilization, hydrophobic interactions, and steric hindrance in protein stabilization. 3. The evolution of lysozyme structure and function will be investigated by determining and comparing the three-dimensional structures of lysozymes that have dissimilar amino acid sequences. In particular, we will continue structural studies of goose egg-white lysozyme and its relationship to chicken and phage lysozymes.